1. Field of the Invention
This invention relates to a transmission path controlling apparatus provided in a communication apparatus (for example, a router or load equalization apparatus) which forms an network, and further to a transmission path controlling method executed by the apparatus as well as a medium on which a transmission path controlling program used in the apparatus is recorded. The method and apparatus may be provided within, for example, an Internet Protocol network (in the following description an Internet Protocol is sometimes referred to simply as IP; accordingly, an Internet Protocol network is referred to simply as IP network).
2. Description of the Related Art
The Internet is intended to handle all communication applications on the internet protocol and is being popularized rapidly at present. Further, the Internet originally has a connectionless network architecture which does not involve establishment of a connection, and is routed to an outgoing path based on a destination address described in an IP packet. In short, in a communication apparatus having the function described, at a point of time when an IP packet arrives at the apparatus, the IP packet is merely transferred to an outgoing path which corresponds to the IP address.
In the Internet having such a network architecture as described above, in order to determine to which outgoing path each IP address should be transferred, a protocol for path determination called routing protocol is handled between communication apparatus.
At present, as an algorithm for the routing protocol, a system which employs the algorithm of Dijkstra is commonly used. However, the routing protocol mentioned has a problem in that a plurality of routes to a destination cannot be selected or the routing protocol is executed only when the network topology varies.
In short, with such a technique as described above, once a route is established, an IP packet is transferred only along the route, and as a result, there is the possibility that chronic congestion occurs.
Further, such a technique as described above has a problem also in that, since a plurality of routes cannot be set, when a certain route suffers from congestion, even if some other route is unoccupied, this unoccupied route cannot be used.
Thus, the following techniques have been proposed.
(1-1) Equal cost multipath technique in the OSPF (Open Shortest Path First)
(1-2) Multipath technique in the IBGP (Internal Border Gateway Protocol)
In particular, the method according to the technique of (1-1) is a method which uses a function of the OSPF, and uses a function capable of laying a plurality of paths having an equal cost from a communication apparatus which serves as a start point to another communication apparatus which serves as an end point to distribute load among the plurality of paths (multipaths).
Meanwhile, the method according to the technique of (1-2) uses a function of the IBGP to lay a plurality of paths and distribute load among the plurality of paths (multipaths).
However, the method which uses a function of the OSPF according to (1-1) above has the following problems.
In particular, there is a restriction in that the multipaths must be equal in cost, and the degree of freedom in path selection is low. Further, since the OSPF is used, the method cannot cope with a variation of the network load on a real time basis.
Also the method which uses a function of the IBGP according to (1-2) above has a restriction in that the multipaths must be equal in cost and has a problem in that the degree of freedom in path selection is low, similarly to the problems of the method which uses a function of the OSPF.
It is to be noted that also a technique has been proposed wherein a path is set in the layer 3 between data processing apparatus which connect networks to each other and load is distributed in a unit of a route in the layer 3 to dynamically provide a traffic balance to improve the network performance (refer to the official gazette of Japanese Patent Laid-Open No. HEI 10-224400). With the technique, however, even if a traffic balance can be provided between networks, load distribution in each network cannot be performed. Further, only load distribution in the layer 3 and in a unit of a route is taken into consideration, and there is the possibility that load distribution control may be complicated.